The present invention relates to material removal devices and methods, and more particularly to disintegration and removal of a cataracted lens from a human or animal eye. There are known instruments used in the removal of cataracts having a sleeve and vibratory needle within the sleeve. Irrigation of the interior of the eye is accomplished through the annular space between the sleeve and the needle, while aspiration is carried out through the lumen in the needle.
The vibratory needle assists in the lens tissue disintegration, also known as phaco-emulsification. The cutting along its axis at a very high frequency. The movement of the vibrating cutting tip causes the lens tissue to disintegrate. As the lens breaks apart, the resulting loose lens particles are aspirated from the capsular bag under vacuum through a conduit in the tubular cutting tip of the vibrating instrument.
U.S. Pat. No. 3,589,363 to Banko and Kelman discloses such a hand held instrument for breaking apart and removing tissue from a body site, such as cataracted lens tissue from a human eye.
Conventional systems are known in which irrigation through the hand held instrument operates on a gravity feed principle, e.g., from an irrigation bottle to the annular space between the sleeve and the needle. Such is exemplified in U.S. Pat. No. 4,465,470. In accordance with its teaching, an eye irrigation solution container is arranged at a higher elevation than the eye. A conduit extends downwardly from the container to a drain at an elevation lower than the eye. Gravity flow of fluid from the container to the drain produces a negative pressure in the interior of the needle to aspirate fluid from the eye. Irrigation/aspiration branches extend from the conduit to a conventional irrigation/aspiration hand held instrument. The instrument has an inner needle-like irrigation tube surrounded by an outer sleeve. Fluid flow is from the container through the conduit to the irrigation branch and into the eye through the annular space between the sleeve and the needle. Aspiration flow is from the eye through the human in the needle and through the aspiration branch, back to the conduit and then to the drain.
Alternatively, aspiration may be controlled by a peristaltic or venturi pump, which provides the vacuum to aspirate fluid and lens material. For instance, plugging the aspiration line to eliminate outflow completely would result in a cloud of unaspirated emulsate obscuring the view within the eye. Aspirating such emulsate is therefore desirable. Even without such a peristaltic or venturi pump, outflow from the eye through the lumen in the tip would still occur because the vibrating phaco tip alone acts as a pump.
The use of so-called zero vacuum is conventional during the sculpting phase of a nucleo fractis phaco-emulsification technique. Even with so-called zero vacuum and very low aspiration rates, however, portions of the posterior capsule of the eye can still be attracted to the phaco tip. When emulsifying close to the posterior capsule with a conventional instrument that irrigates through the annular space between the sleeve and needle and aspirates through the lumen of the needle, there is a danger that the capsule may be accidently touched with the aspiration tip of the needle. In that case, the portion of the capsule that is touched may be sucked into the opening of the needle, resulting in breakage of the capsule.
It would therefore be desirable to devise a surgical instrument with which a sculpting phase of a nucleo phaco-emulsification technique avoids attracting the posterior capsule to the phaco tip and actually pushes the capsule away from the vibrating tip.